In my understanding, as long as internet is up, bitcoin will survive. If internet gets destructed, that would be more catastrophic than bitcoin's destruction.
Which isn't entirely possible (or at least very unlikely). If the internet gets destroyed, something much worse is in for us.
there will always be some sort of connectivity. unless all our electronic devices are non functional, there will always be a way. transactions may take time to post across the world but would still be more effective than any commercial options. bitcoin value would skyrocket.